Nicotine induces tyrosine hydroxylase in superior cervical ganglion. This action is facilitated by blockade and inhibited by activation of muscarinic receptors. The antagonistic effect of muscarinic agents on the increase of TH activity elicited by nicotinic receptor agonists appears to be mediated by dopamine presumably stored in the SIF cells. In addition, dopamine receptor agonists prevent the induction of TH by nicotine, whereas prior depletion of dopamine stores by reserpine facilitates the action of nicotine on TH induction in decentralized ganglia.